The present invention relates to improvements in apparatus for manufacturing discontinuous cross-section structural board from granular materials.
In the manufacture of discontinuous cross-section structural board from granular material, it is conventional to use apparatus as described in U.S. Pat. No. 3,229,009, issued Jan. 11, 1966, entitled METHOD AND APPARATUS FOR FORMING COMPOSITION BOARD and U.S. Pat. No. 3,142,185, issued July 28, 1964, entitled PISTON STROKE ADJUSTMENT. In apparatus of this type, particulate material such as various types of wood sawdust, wood chips, wood scraps, and the like, which have been comminuted, are used in the formation of structural members. The particulate material is conventionally mixed with a thermosetting adhesive and is then forced through a mold. In the molding of these products, economic factors make it desirable to obtain as high a rate of production as possible. In forming structural board by this process, it is necessary to maintain the particulate material in a state of compression while heat penetrates the material causing the thermosetting adhesive to bond the particles. Once this bonding is complete, the compression may be removed.
One problem encountered in developing equipment for molding these materials is that the rate of heat penetration varies with numerous factors such as mold temperatures, section thickness, specific heat of the material, moisture content, particle size, material distribution in the mold, and density. In addition, it has been found that in lower density boards, the pulsating forces of the plunger forcing the material through the mold will cause weakening of internal bonds of the particulate material after the initial molding process. If the length of the mold in terms of direction of material travel is increased to reduce the effect of the plunger impact on the material as it exits the mold, mold friction is increased, which in turn may increase the density of the material beyond the desired amount. Further, the entrapment of steam and other gases along this increased mold length may delay curing of the adhesives.
Therefore, there exists a need for an improved molding apparatus capable of curing the extruded material while controlling density and preventing weakening of the material due to the pulsating forces introduced by the plunger.
The present invention provides an improved cooker apparatus which is positioned at the discharge end of the mold and which is provided with an upper cooker plate conforming to the upper surface of the material exiting the mold. Longitudinally extending heaters are provided in contact with the upper cooker plate. A lower cooker surface is defined by a plurality of longitudinally extending bars which contact the lower surface of the material in areas spaced between the legs thereof. The upper cooker plate may be adjusted relative to the lower bars such that compression can be varied longitudinally and transversely across the material. In addition, spaces are provided between the lower bars sufficient to allow loose material to fall out of the cooker and steam and other gases to escape from the material as it cures in the cooker.